Field of the Invention
Embodiments of the present invention relate to a method for selectively removing a plurality of target objects after dry etching by continuously changing the composition of a stripping solution.
Description of the Related Art
In the processing of common microelectromechanical systems (MEMS) and the processing of a semiconductor device, there are a large number of examples in which a silicon substrate is processed so as to be penetrated and in which a structure having depth comparable to the thickness of the silicon substrate is processed. Such a technique for microfabricating a semiconductor device is employed for the processing of a silicon substrate used for a liquid ejection head.
As a liquid ejection head used for a liquid ejection apparatus, such as an ink jet printer, a structure including a flow passage-forming member arranged on a silicon substrate is known. The flow passage-forming member includes an ejection orifice that ejects a droplet and a liquid flow passage communicating with the ejection orifice. Typically, a plurality of liquid flow passages are arrayed. A liquid ejection energy production element is arranged on the silicon substrate so as to eject a droplet from the ejection orifice by energy produced in the liquid ejection energy production element. Furthermore, a plurality of supply ports communicating with the liquid flow passages, and a common liquid chamber communicating with the supply ports are arranged on the silicon substrate.
In this structure, for example, a liquid is heated and bubbled by thermal energy from the liquid ejection energy production element, such as an ejection heater, to eject from the ejection orifices. In this case, the liquid flow passages are supplied with the liquid from the supply ports. The supply ports are supplied with the liquid from the common liquid chamber.
The supply ports and the common liquid chamber are formed by etching the silicon substrate or an insulating film of a wiring layer on a surface. Nowadays, there are growing instances where etching treatment is changed from wet etching, which has been mainly employed, to dry etching, in particular, reactive ion etching with high anisotropy in order to achieve the miniaturization and higher density of a liquid ejection head.
Typically, a resist may be used as a mask material for dry etching. In dry etching, the impact of plasma often forms a transformed layer on a surface of the resist (see FIG. 5B). The transformed layer is a layer of the resist that has been structurally changed. The transformed layer is not dissolved in a resist-stripping solution, in some cases.
In the etching of silicon and a silicon oxide film, a deposited reaction product (hereinafter, also referred to as a “deposited film”) is often formed on a resist surface and substrate surfaces (including an etched side surface) (see FIG. 5B). This is attributed to the fact that a dry etching technique for the foregoing materials is a system in which etching is performed in the vertical direction while the deposited film is formed on a side wall to protect the substrate. An example of a technique for etching silicon to form a high-aspect-ratio structure is the Bosch process in which SF6 and C4F8 are alternately used. In the process, a fluorocarbon-based polymer produced from C4F8 adheres to the side wall to inhibit etching in the direction of the side wall. A SiFx-based compound containing silicon that has been etched can be contained in the deposited film. In this specification, a compound formed from plasma described above and a compound formed by etching an object are collectively referred to as “reaction products”. Depositions (deposited films) of these reaction products are not dissolved in a resist-stripping solution, in some cases.
As well as the resist, the transformed layer and the deposited film formed during the etching need to be removed so as not to cause damage to an underlying material. However, when the transformed layer and the deposited film are removed with a resist-stripping solution, the transformed layer and the deposited film can be left as residues after a stripping operation. U.S. Pat. No. 7,837,887 discloses a method that includes removing a mask material by ashing and removing a residue with a stripping solution (EKC, registered trademark).